With conventional engine analysers, for example of the type disclosed in British Patent Specification No. 1166233, the voltage on the primary of the ignition coil is monitored and used to inhibit the igniton pulse on a specified cylinder, so that the performance of each individual cylinder can be analysed.
With conventional inductive discharge ignition systems the rise time of the ignition pulse is typically of the order of 20 .mu.s. It is consequently possible, upon sensing the pulse on the primary of the ignition coil, to short out the ignition device and inhibit the spark on that cylinder.
With capacitor discharge ignition systems, the rise time of the ignition pulse is only of the order of 2 .mu.s. With a conventional engine analyser it is not possible to inhibit such a pulse before the ignition device is fired.